Microinjection
offers the possibility to test the function of molecules in cells.
Here an ascidian egg is microinjected with a mixture of proteins
from the inside of sperm, one of which will cause the calcium
stored in the endoplasmic reticulum to be released. The released
calcium stimulates the egg to begin embryogenesis. Alex McDougall.With
the use of fluorescent dyes that change their properties when
calcium is present it is possible to measure the level of calcium
in living cells. In this clip the level of calcium in the egg
following microinjection is shown (images to the right) together
with simultaneous bright field images of the egg in order to follow
the shape change (the cortical contraction) that the calcium wave
induces. We chose red and orange to represent high calcium levels
high levels and blue calcium respectively. About 30 seconds following
microinjection the level of calcium rises in the egg and a further
30 seconds after that the egg changes shape. The calcium rises
first in a discrete region of the egg cortex and then spreads
through the whole egg. These are termed calcium waves. In ascidians
these waves are repeated about a dozen times over a period of
about 30 minutes. Similar periodic waves are found during mammalian
fertilization during a period of about 3 hours following fertilization.
Alex McDougall. link to lab |
